Numerous types and configurations for secondary batteries have been developed to improve various aspects of energy storage, and particularly the ratio of weight or volume to capacity. Among various alternative configurations, cell stacks in which bipolar electrodes separating anode from cathode compartments have held considerable promise in the reduction of cell size, and there are numerous such systems known in the art.
For example, U.S. Pat. No. 5,264,305 describes a cell system in which zinc is used as one redox element, and in which a bipolar plate construction with horizontally disposed battery components provides electrical current. While such configurations are typically less space-consuming than conventional zinc-based configurations, several disadvantages still persist. Among other problems, the ratio of weight or volume to capacity is still relatively poor.
In another example, bipolar electrodes may be employed in zinc air batteries as described in “Bipolar zinc-air secondary battery” by C. Schlatter, Ch. Comninellis, 45th annual meeting of ISE, Porto, Portugal, Proc. VII-109, Vol. 2, (1994). While the use of a zinc air couple significantly reduces the weight on such batteries, oxidation problems of the membranes, and particularly deposit formation are relatively common.
To circumvent at least some of the problems with limited capacity and oxidative damage of bipolar electrodes, zinc bromine systems have been implemented in which zinc and bromine form a redox couple, and in which a bipolar electrode separates anode and cathode compartments. Such batteries are known to exhibit a 2–3 fold increased power density when compared to traditional lead-acid batteries. Moreover, the capacity is typically only limited by the amount of catholyte and anolyte. However, the corrosive nature of bromine tends to limit the range of materials from which bipolar electrodes may be manufactured. Furthermore, such systems are environmentally problematic during manufacture, maintenance, and disposal.
In still other battery systems with bipolar electrodes, and especially where the electrolyte is an acidic electrolyte, additional problems arise. Typically, carbon or graphite electrodes are readily oxidized under standard operating conditions. Consequently, most, if not all of such systems require development and implementation of composite bipolar electrodes, which significantly tends to increase production cost. Moreover, at least some of those systems require additional catalyst to promote oxidation of one of the elements in the redox couple.
Thus, although there are numerous electric devices with bipolar electrodes known in the art, all or almost all of them suffer from one or more disadvantage. Therefore, there is still a need to provide compositions and methods for electric devices with improved bipolar electrodes.